Electrodes that can be implanted for a long time into the central nervous system (CNS) have a wide application. In principle, all brain nuclei can be recorded from or stimulated by such electrodes and their functions monitored and controlled. Stimulation of the brain or spinal cord can be of particular value in situations when brain nuclei are degenerated or injured. Monitoring brain activity can be useful if linked to drug delivery or other measures such as electrical stimulation. Electrodes can also be used to lesion specific sites in tissue. To record and stimulate brain structures various forms of implanted electrodes have been developed and used in the past. For a long time implantable electrodes have been used for symptomatic treatment of Parkinson's disease (U.S. Pat. No. 6,647,296 B), chronic pain and control of spinal function.
Single relatively stiff electrodes with one or multiple sites for recording and/or stimulation disposed along their shafts (US 2003083724 A), twisted wire electrodes, multi-channel electrodes consisting of a multitude of parallel wires (WO 03077988 A, U.S. Pat. No. 6,171,239 B), multi-array needle-like electrodes (U.S. Pat. No. 6,171,239 B) protruding from a base plate are known in the literature. Known multichannel electrode arrays with electrodes protruding from a base plate consist of relatively stiff wires or needle-like electrodes that allow recordings/stimulation only in superficial parts of the brain. Further electrodes of this kind are disclosed in US 20060178709 A, US 20050228249 A, U.S. Pat. No. 5,366,493 A, and U.S. Pat. No. 6,597,953 B.
A particular problem with known electrodes of this kind is their retention at the desired site in tissue, in particular in the brain, over an extended period of time, such as from one week to one month and event for one year or more. Dislocation after insertion may make them entirely useless. For instance, implanted wire electrodes used in pain control are not equipped with anchoring means capable of retaining them in their original position close to the target cells. Consequently, they are often dislocated after insertion into brain areas that exhibit constant rhythmic movements due to breathing and heart activity, like the brain stem or the spinal cord resulting in therapy failure.
Another problem with known electrodes is damage of brain or other soft tissue caused during insertion.
Known multi-channel electrode arrays with stiff electrodes are vulnerable to tissue acceleration, for example when the patient's head is suddenly moving. The resulting shearing forces may irritate the tissue or even kill cells adjacent to the electrode. In addition, there has not been provided a solution to the problem of precisely positioning multiple ultra thin and flexible electrodes deep into the central nervous system.